Thermal performance evaluation of artificial protective coatings applied to steam surface condenser tubes

Goodenough, John L. (2013-12)

Thesis (MScEng)-- Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: The coating thermal conductivity, the effective coated-tube thermal conductivity and the coating factor of three artificial protective coatings (APCs) applied to condenser tubes are experimentally evaluated. This testing broadens the limited available knowledge of these coatings, which is necessary for effective condenser refurbishment and operation. The coatings are applied to 25.4 mm brass tubes at thicknesses of 44, 46, 50, and 130 μm. Steady state heat transfer tests are performed on these tubes fitted in a double-pipe counter-flow heat exchanger, with heated water in the annulus and coolingwater inside the tube. The experimentally determined thermal conductivities of the coatings range from 0.5 to 2.3 W/m·K. The effective coated-tube conductivity and the coating factor depend on the tube material and size, as well as the coating thickness. A one-dimensional condenser model is used to parametrically investigate the relative overall effect on condenser performance. From these results, coating guidelines for Admiralty brass tubes are proposed in terms of the minimum and maximum coating conductivity and thickness. The effect of the coating on the thermal performance is equivalent to a Heat Exchange Institute (HEI) cleanliness factor of at least 0.85, when adhering to these guidelines. APCs provide a layer of protection against corrosion, erosion and fouling and can preferentially fill tube-wall pits. They can therefore be used to extend the condenser life-span effectively, but, to ensure minimal impact on the overall condenser performance, the coating thickness and conductivity must be carefully controlled and verified experimentally.

AFRIKAANSE OPSOMMING: Die termiese geleidingsvermoë, die effektiewe termiese geleidingsvermoë van bedekte buise en die bedekkingsfaktor van drie kunsmatige beskermingsbedekkingslae wat op kondensorbuise aangewend word, word eksperimenteel geëvalueer. Hierdie evaluering verbreed die beperkte beskikbare kennis oor sodanige bedekkingslae, wat nodig is vir effektiewe kondensor herinrigting en bedryf. Die lae word teen diktes van 44, 46, 50 en 130 μm in 25.4 mm geelkoperbuise aangewend. Warmteoordragstoetse by gestadigde toestande word gedoen op hierdie buise in ’n dubbelpyp-teenvloeiwarmteoordraer, met verhitte water in die annulus en verkoelingswater binne-in die buis. Die eksperimenteel bepaalde termiese geleidingkoëffisiënte wissel tussen 0.5 tot 2.3 W/m·K. Die effektiewe geleidingsvermoë en bedekkingsfaktor hang af van sowel die buis se materiaal en grootte sowel as die dikte van die bedekkings. ’n Eendimensionele kondensormodel word gebruik om die algehele effek van hierdie beskermingsbedekkingslae op kondensorwerkverrigting parametries te ondersoek. Riglyne ten opsigte van aanwending van beskermingslae vir buise van “Admiralty” geelkoper word verskaf in terme van die minimum en maksimum geleidingsvermoë en dikte van bedekkingslae. Met behulp van hierdie riglyne word ’n “Heat Exchange Institue” (HEI) ekwivalente skoonheidsfaktor van minstens 0.85 op ’n nuwe buis behaal. Hierdie kunsmatige bedekkingslaeslae bied beskerming teen korrosie, erosie en bevuiling en kan klein kuile in die buiswand vul. Hulle kan dus gebruik word om die lewensduur van die kondensator te verleng, maar hul dikte en geleidingsvermoë moet noukeurig beheer word en moet eksperimenteel geverifieer word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85698
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